Early in the day on July 12, 2000, a dozen or so commuters in the Jardim Botanico district of Rio de Janeiro had the misfortune of boarding Bus #174. A perfectly nice bus in many respects, #174 was possessed of one significant flaw -- on that July morning it was hijacked by a distraught, confused, and possibly high young man, sparking a protracted police standoff with tragic consequences. It's what Rod Serling might have called a morning commute to destiny.

Jose Padilha's "Bus 174" relates the bus hijacking and ensuing hostage crisis in excruciating detail, using interviews with participants and miles of news footage shot during the event. (So now we know: America is not the only country with a television news media that thirsts for blood.) Close-ups, wide angles, reversals, and helicopter shots; any fiction feature could not hope for more or better coverage, and "Bus 174" is expertly edited to give a sense of the multiplicity of viewpoints and the subtle differences that each vantage allows. There is much confusion, and often it is not clear precisely what is going on, other than something terrible: a man holding a gun to a woman's head, a woman crying, people outside pointing guns at the man, the man crying, the man yelling.

Brandishing his pistol with his arm around the neck of a hostage, the hijacker, named Sandro, shouts out the bus window, to no one and everyone, "This is no action movie!" He's right on that account, at least. Padilha's film moves in fits and starts, sometimes with agonizing slowness, then with a lot of things happening all at once, a pace that echoes the queasy movement of the standoff. To give viewers some breathing room, the film steps back from the standoff to provide some context, and to show how Sandro, a former street kid, came to find himself in this situation.

A Brazilian sociologist and a social worker describe the various factors by which street kids become street kids, and they discuss how these children are unbounded by family, or by any measure of civil society. They are bothersome and unwanted, an open secret and an open sore in a country that is unwilling and ill-prepared to deal with them. Untethered from society, we are told that street kids "lose contact with their past." As if to remedy this lack of history, the film examines the short, unhappy life of Sandro the hijacker, and with thorough research it uncovers a story that could not have been more tragic if it were scripted. Sandro grew up in a poor Rio neighborhood without a father. When he was 10, he witnessed the stabbing death of his mother, a shopkeeper pregnant with twins. He ran away from his caretaker aunt and joined a street gang. He sniffed glue, landed in prison, escaped, got arrested again, and then we start to lose track of his travails, they are so sadly the same. In this regard and elsewhere, the story line of "Bus 174" would benefit from a more aggressive paring of such details. As it is, the almost unremitting litany of painful experience is exhausting.

Aside from the loss of his mother, one other especially terrible incident stands out in Sandro the hijacker's early life: the unprovoked massacre (by assailants unknown, likely the police) of several of his street kid friends in the district of Candelaria. A teenaged Sandro witnesses this, too. Can there be any clearer indication, then, that violence begets violence? It is all he has ever known. After these scenes, viewers might sprout a small flower of sympathy for this poor devil and catch a slight case of Stockholm Syndrome. Though his means are frightening and his ends indeterminate, it is clear Sandro is as much victim as perpetrator.

This point is driven home by the angry mob that surrounds the siege area, the aggressive reporters and camera crews, and the sloppy decision-making of the police. One does not have a great deal of confidence in the forces handling the situation. (For a country that was not so long ago under a military dictatorship, one would think the authorities would have a better handle on how to control something like this.) It is every bit the circus that was portrayed in another, funnier siege film, "Dog Day Afternoon." The unfortunate resolution of the incident, occasioned by nothing so much as a royal police muck-up, unfolds before our eyes, frame by chilling frame.

There is an icy, clinical chill to much of "Bus 174," a tone well-suited to such goings on, if not to a fun night out at the movies. "Bus 174" is one of the most singularly depressing documentaries (or films, period) to grace the independent circuit in some time. The tone is set in the film's opening minutes; as an aerial camera glides over the pristine blue waters and lush green parks of Rio's shoreline, a series of voiceovers by drug addicts and street people, intoning the brutal experiences of their lives, belie the beauty on-screen. For two agonizing hours, Padilha picks at the social scabs of South American's largest nation, and applies no soothing balm. What's wrong with a country like Brazil? Here are a few things.